The present invention relates to an electromagnetic valve control system for electromagnetically controlling a valve to open and close an intake or exhaust port through which the interior and exterior of an engine cylinder communicate with each other.
When fuel is burned in combustion chambers in the cylinders of an engine, the pistons in the cylinders are successively lowered to cause the connecting rods to rotate the crankshaft. A conventional control system for controlling intake and exhaust valves for introducing an air-fuel mixture into and discharging exhaust gases from the combustion chambers includes a camshaft rotatable about its own axis by the crankshaft through a timing belt and pulleys. The intake and exhaust valves are moved to open and close intake and exhaust ports by rocker arms slidably held against cam surfaces of the camshaft.
While the engine is in operation, it is not possible to vary the timing at which the intake and exhaust valves open and close the intake and exhaust ports. Therefore, the timing of opening and closing the intake and exhaust ports with the intake and exhaust valves is selected such that the engine operates with high efficiency when it rotates at a certain speed.
More specifically, an intake valve is opened a crankshaft angle ranging from 20.degree. to 30.degree. ahead of the top dead center (TDC) of the associated piston, and closed a crankshaft angle ranging from 50.degree. to 60.degree. after the bottom dead center (BDC) of the piston.
An exhaust valve is opened a crankshaft angle ranging from 50.degree. to 60.degree. ahead of the bottom dead center of the piston, and closed a crankshaft angle ranging from 20.degree. to 30.degree. after the top dead center of the piston.
With such timing settings, however, the intake valve remains open for a certain period of time after the bottom dead center. When the engine speed is low, since the inertial force of intake air is small, an air-fuel mixture which is once introduced into the cylinder tends to flow back out of the cylinder through the intake port during that period of time. As a result, the engine power output is reduced. Conversely, when the engine speed is high, because the inertial force of intake air is large, intake air continuously flows into the cylinder even after the piston has started to move up in the compression stroke. Since the intake valve is then closed while intake air is still flowing into the cylinder, the volumetric efficiency is lowered, and so is the engine power output.
Japanese Laid-Open Patent Publications Nos. 58-183805 and 61-76713 disclose valve control systems for actuating intake and exhaust valves with electromagnetic means. However, the disclosed valve control systems have not been addressed to the above problems.